The invention relates to the metering of flows of steam to steam consumers, particularly in the circumstance wherein there are large changes in demand over the course of time.
Steam-supply facilities suffer adverse economic consequence from the fact that the steam-metering system for each customer has a limited range of flowmeasuring capability, selected for optimum efficiency for the predominant range of demand for the particular customer. This being the case, the flow-measuring capability is inadequate to respond to a low-demand situation, with the result that much of the customer's use of low-demand steam is not metered and therefore cannot be billed. To a degree, the same metering deficiency applies to overload-demand situations which are beyond the efficient metering range of the system.
It has been proposed to meet the problem of limited-demand flow-measuring capability by employing two separate supply lines in parallel to each customer, one of the lines having its control valve and flow-measuring means to provide optimized metering for a normal or high rate of flow, for periods of high demand, and the other line being similarly equipped but providing optimized metering for the low-demand situation, the supply connection to the customer being via one or the other of these lines. Such systems have been less than satisfactory for various reasons, including (1) an inability to transfer smoothly from use of one supply line to use of the other, and (2) undue response to transient changes in demand. And although the different approaches of Pegrum U.S. Pat. No. 3,164,726, Cramer U.S. Pat. No. 3,612,500 and Kruto U.S. Pat. No. 4,425,930 deal with problems of extended-range response in other arts, none of them is suggestive of a solution for the above-indicated metering problem for the commercial steam supplier.